Silicon wafer and method for producing silicon single crystal

ABSTRACT

A method for growing a silicon single crystal ingot by a Czochralski method, which is capable of providing silicon wafers having very uniform in-plane quality and which results in improvement of semiconductor device yield. A method is provided for producing a silicon single crystal ingot by a Czochralski method, wherein when convection of a silicon melt is divided into a core cell and an outer cell, the silicon single crystal ingot is grown under the condition that the maximal horizontal direction width of the core cell is 30 to 60% of a surface radius of the silicon melt. In one embodiment the silicon single crystal ingot is grown under the condition that the maximal vertical direction depth of the core cell is equal to or more than 50% of the maximal depth of the silicon melt.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/741,746, filed Dec. 19, 2003, which claims priority to and thebenefit of Korea Patent Applications No. 2002-0082733 filed on Dec. 23,2002 and No. 2003-0080998 filed on Nov. 17, 2003, both in the KoreanIntellectual Property Office, priority of which are claimed herein.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method for growing a silicon singlecrystal ingot based on a Czochralski method, and more particularly to amethod of growing a silicon single crystal ingot for producing siliconwafers having uniform in-plane quality.

(b) Description of the Related Art

In general, methods for growing a silicon single crystal ingot based ona Czochralski method use a grower as shown in FIG. 1, which is asectional view showing the inside of a general grower for silicon singlecrystal ingots. As shown in FIG. 1, poly-crystalline silicon is loadedinto quartz crucible 10 and melted into silicon melt SM by heatirradiated from heater 30, and then silicon single crystal ingot IG isgrown from a surface of silicon melt SM.

When silicon single crystal ingot IG is grown, quartz crucible 10 isascended such that a solid-liquid interface maintains the same heightwhile rotating an axis 20 supporting quartz crucible 10, and siliconsingle crystal ingot IG is pulled up while rotating it in an oppositedirection to that of quartz crucible 10 with the same axis center as therotation axis of quartz crucible 10.

In addition, to facilitate silicon single crystal ingot growth, an inertgas such as Ar gas can be generally injected into a grower and thendischarged from the grower.

In such conventional silicon single crystal ingot production methods,heat shield 40 and a cooling-water jacket (not shown) for adjusting atemperature gradient of silicon single crystal ingot IG is installed.Conventional techniques using the heat shield are disclosed in KoreanPatent Registration No. 374703, Korean Patent Application No.2000-0071000, and U.S. Pat. No. 6,527,859.

However, there is a limit to production of a silicon single crystalingot and silicon wafers having uniform quality in a radial directionwhen only adjusting the temperature gradient of silicon single crystalingot IG. Therefore, there is a keen need for new techniques forproducing the silicon single crystal ingot and silicon wafers havinguniform quality in a radial direction.

In particular, when semiconductor devices are fabricated using siliconwafers having nonuniform quality in a radial direction, which areprepared according to the conventional techniques, the nonuniformity ofquality of the silicon wafers is increased when the silicon wafers areheat-treated several times in a fabrication process of the semiconductordevice. This results in a reduction of semiconductor device yield.

SUMMARY OF THE INVENTION

In accordance with the present invention, a silicon single crystal ingotis provided which has uniform quality in a radial direction so thatsilicon wafers having uniform in-plane quality can be produced.

The present invention has one motivation to determine critical processvariables for growing a silicon single crystal ingot having uniformquality in a radial direction.

The present invention has another motivation to determine optimalprocess conditions for growing a silicon single crystal ingot havinguniform quality in a radial direction.

The present invention has still another motivation to improvesemiconductor device yield by producing silicon wafers having uniformin-plane quality.

There is provided a method for producing a silicon single crystal ingotby a Czochralski method, which is capable of uniformly controllingquality characteristics such as oxygen and point defect distributionscontained in the silicon single crystal ingot and silicon wafers byeffectively controlling convection distribution of a silicon melt withina quartz crucible such that distribution of oxygen and heat in thevicinity of a solid-liquid interface where a silicon melt iscrystallized become uniform.

According to an aspect of the present invention, there is provided amethod for producing a silicon single crystal ingot by a Czochralskimethod, wherein when convection of a silicon melt is divided into a corecell and an outer cell, the silicon single crystal ingot is grown underthe condition that the maximal horizontal direction width of the corecell is 30 to 60% of a surface radius of the silicon melt.

In an exemplary embodiment the silicon single crystal ingot is grownunder the condition that the maximal vertical direction depth of thecore cell is equal to or more than 50% of the maximal depth of thesilicon melt.

In an exemplary embodiment the silicon single crystal ingot is grownunder the condition that the maximal vertical direction depth of thecore cell is 80 to 95% of the maximal depth of the silicon melt.

In an exemplary embodiment the width or depth of the core cell iscontrolled by adjusting an amount of inflow of Ar gas flowing into theinside of a silicon single crystal ingot growth apparatus, a rotationspeed of a quartz crucible containing the silicon melt, or a rotationspeed of the silicon single crystal ingot.

Specifically, the width or depth of the core cell is increased when theamount of inflow of the Ar gas is increased, the rotation speed of thequartz crucible is decreased, or the rotation speed of the siliconsingle crystal ingot under growth is increased.

According to another aspect of the present invention, a silicon wafer isprovided wherein a standard deviation of in-plane interstitial oxygenconcentration distribution is equal to or less than 0.1.

In an exemplary embodiment, point defect concentration contained in thesilicon wafer is 10¹¹-10¹³/cm³.

In an exemplary embodiment an in-plane variation of delta interstitialoxygen concentration (delta [Oi]), which is a difference betweeninterstitial oxygen concentration after first heat-treating the siliconwafer at a temperature of 800° C. for 4 hours in an atmosphere of 95%nitrogen and 5% oxygen and then heat-treating the silicon wafer at atemperature of 1000° C. for 16 hours in an atmosphere of 95% nitrogenand 5% oxygen, and interstitial oxygen concentration before the firstheat-treatment, is equal to or less than 0.5 ppma (parts per millionatoms) (or 0.25×10¹⁷/cm³).

In an exemplary embodiment a difference between maximum and minimum ofscale bars in an image obtained by minority carrier life time (MCLT)scanning, after first heat-treating the silicon wafer at a temperatureof 800° C. for 4 hours in an atmosphere of 95% nitrogen and 5% oxygenand then heat-treating the silicon wafer at a temperature of 1000° C.for 16 hours in an atmosphere of 95% nitrogen and 5% oxygen, is equal toor less than 10.

In an exemplary embodiment the difference between maximum and minimum ofscale bars in an image obtained by a MCLT scanning after the first andsecond heat-treatments is equal to or less than 5, and in a furtherembodiment, 3.

According to still another aspect of the present invention, there isprovided a silicon single crystal ingot wherein a standard deviation ofinterstitial oxygen concentration distribution in a radial direction ofthe silicon single crystal ingot is equal to or less than 0.1.

In an exemplary embodiment a concentration of point defects contained inthe silicon single crystal ingot produced according to the method of thepresent invention is 10¹¹-10¹³/cm³.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing the inside of a general siliconsingle crystal ingot growth apparatus.

FIG. 2 is a schematic view showing convection distribution of siliconmelt SM according to a conventional method.

FIG. 3 is a schematic view showing convection distribution of siliconmelt SM according to the present invention.

FIG. 4 a is a schematic view showing convection distribution of asilicon melt in an experimental example 1.

FIG. 4 b is a schematic view showing convection distribution of asilicon melt in an experimental example 2.

FIG. 4 c is a schematic view showing convection distribution of asilicon melt in an experimental example 3.

FIG. 5 a is a graph showing a result of measurement of distribution ofinitial interstitial oxygen concentration [0i] with respect to adistance in a radial direction in the silicon wafer according to anembodiment of the present invention.

FIG. 5 b is a graph showing a result of measurement of a delta [0i],which is a difference between interstitial oxygen concentration beforeheat-treatment and interstitial oxygen concentration afterheat-treatment, with respect to a distance in a radial direction in thesilicon wafer according to an embodiment of the present invention.

FIG. 5 c is an image showing a result of MCLT scanning afterheat-treatment for the silicon wafer according to an embodiment of thepresent invention.

FIG. 6 a is a graph showing a result of measurement of distribution ofinitial interstitial oxygen concentration [0i] with respect to adistance in a radial direction in the silicon wafer according tocomparative example 1.

FIG. 6 b is a graph showing a result of measurement of a delta [0i],which is a difference between interstitial oxygen concentration beforeheat-treatment and interstitial oxygen concentration afterheat-treatment, with respect to a distance in a wafer radial directionin the silicon wafer according to comparative example 1.

FIG. 6 c is an image showing a result of MCLT scanning for the siliconwafer according to comparative example 1.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings.

The present invention pays attention to the fact that convectiondistribution of a silicon melt should be controlled in order to grow asilicon single crystal ingot having uniform quality in a radialdirection, starting from the perception that growth of the siliconsingle crystal ingot having the uniform quality in the radialdirection-based on the Czochralski method is not achieved only by anadjustment of a temperature gradient in the ingot and an adjustment ofshape of a solid-liquid interface.

FIG. 2 is a schematic view showing convection distribution of siliconmelt SM according to a conventional method. When silicon single crystalingot IG is grown according to the conventional method, the silicon meltSM has convection distributions A and B as shown in FIG. 2.

Specifically, the convection distributions of silicon melt SM arelargely divided into an outer cell B where silicon melt SM is circulatedin a way that the silicon melt follows a bottom and a side wall ofquartz crucible 10, rises toward a surface of the silicon melt, andflows toward silicon single crystal ingot IG along the surface of thesilicon melt, and core cell A where silicon melt SM is circulated in alower adjacent portion of silicon single crystal ingot IG along an innerincline plane of outer cell B.

At this time, since the width of core cell A does not deviate from anedge of silicon single crystal ingot IG and the depth of core cell Adoes not reach half of the maximal depth of the silicon melt, the sizeof core cell A is relatively even smaller than that of outer cell B. Inthe prior art, silicon single crystal ingot IG is grown under the statethat the size of core cell A is very small without special efforts toenlarge the size of core cell A.

Under such circumstances, as described in Gawanishi et al., “Meltquenching technique for direct observation of oxygen transport in theCzochralski-grown Si process”, Journal of Crystal Growth, Vol. 152,1995, pp 266-273, since oxygen contained in outer cell B causes anunstable balance of interstitial oxygen concentration between the centerportion and the edge portion of the ingot, the distribution ofinterstitial oxygen concentration at the vicinity of a solid-liquidinterface becomes nonuniform.

In addition, as heat distribution become nonuniform due to a difficultyin sufficient heat supply to the solid-liquid interface, thesolid-liquid interface forms convex shape (a) curved toward the siliconsingle crystal ingot in an edge portion of the solid-liquid interface,and concave shape (b) curved toward the silicon melt in a center portionof the solid-liquid interface. Therefore, the silicon single crystalingot IG was grown under the state that the solid-liquid interface had anonuniform interface of convex (a)-concave (b)-convex (a) shapes as awhole.

The silicon wafer, which is sliced and polished from the silicon singlecrystal ingot IG grown by the above-described conventional method,exhibits a nonuniform quality characteristic in a radial direction ofthe silicon wafer.

FIG. 3 is a schematic view showing convection distribution of siliconmelt SM according to an embodiment of the present invention. As shown inFIG. 3, when convection of the silicon melt within the quartz crucibleis divided into core cell Ao and outer cell Bo, convection distributionof the silicon melt is controlled such that maximal horizontal directionwidth Wmax of core cell Ao is 30 to 60% of a surface radius of thesilicon melt.

In addition to the control of the maximal horizontal direction width ofcore cell Ao, the convection distribution of the silicon melt iscontrolled such that maximal vertical direction depth Hmax of core cellAo of the silicon melt convection distribution is equal to or more than50% of the maximal depth of the silicon melt.

At this time, the convection distribution of the silicon melt ispreferable controlled such that maximal vertical direction depth Hmax ofcore cell Ao is 80 to 95% of the maximal depth of the silicon melt.

As described above, when maximal horizontal direction width Wmax andmaximal vertical direction depth Hmax of the convection of the siliconmelt, particularly, core cell Ao, are controlled to have appropriatesizes, the solid-liquid interface can be made such that it has a convex(a)-convex (a)-convex (a) shape curved toward the silicon single crystalingot, i.e., a single convex shape.

In addition, as described above, by appropriately controlling the sizesof core cell Ao and outer cell Bo, the silicon melt existing in lowtemperature region TI of the bottom of the quartz crucible moves to hightemperature region Th of a lower portion of a side wall of the quartzcrucible along outer cell Bo, is supplied with sufficient heat from hightemperature region Th, and then moves to silicon single crystal ingot IGalong a surface of the silicon melt. In other words, the cold siliconmelt in low temperature region TI having an effect on the solid-liquidinterface by rising straight along core cell Ao can be prevented.

In addition, as an interface between core cell Ao and outer cell Bo iswidely formed, heat exchanging region Trans, where high temperature heatfrom outer cell Bo is transferred to core cell Ao, is widely formed.Therefore, stable convection of core cell Ao and outer cell Bo can beachieved along with active heat exchange between core cell Ao and outercell Bo.

A silicon wafer can then be sliced and polished from the silicon singlecrystal ingot IG grown by the above-described the method in accordancewith the present invention. The resulting silicon wafer would then havea standard deviation of in-plane initial interstitial oxygenconcentration [Oi], which is equal to or less than 0.1.

Here, a smaller standard deviation of in-plane initial interstitialoxygen concentration [Oi] means more uniform distribution of theinterstitial oxygen concentration. A standard deviation of 0 means thatthe in-plane interstitial oxygen concentration is completely uniform,which is the most ideal case. Therefore, it is meaningless to define thelowest limit of the standard deviation, and a smaller standard deviationis desirable.

In addition, when the interstitial oxygen concentration is measuredafter the silicon wafer prepared according to the present invention isfirst heat-treated at a temperature of 800° C. for 4 hours and is thenheat-treated at a temperature of 1000° C. for 16 hours in an atmosphereof 95% nitrogen and 5% oxygen as heat-treatment conditions, from whichoxygen precipitation results (reaction: Si_(si)+2O_(i)+V_(si)→SiO₂), adelta [Oi] indicating a difference between interstitial oxygenconcentration before heat-treatment and that after heat-treatment has avariation which is equal to or less than 0.5 ppma in a wafer plane.

Here, the first and second heat-treatments is an example of aheat-treatment cycle for confirming an oxygen precipitationcharacteristic of the silicon wafer dependent on the interstitial oxygenconcentration and point defect distribution. However, the presentinvention is not limited to this heat-treatment cycle.

A smaller variation of in-plane delta [Oi], which is desirable, meansmore uniform quality of a silicon wafer. A variation of in-plane delta[Oi] of 0 shows an ideal case. Therefore, it is meaningless to definethe lowest limit of the standard deviation.

Further, a difference between a maximum and minimum of a scale bar in animage obtained as a result of MCLT scanning after first heat-treatingthe silicon wafer prepared according to the present invention at atemperature of 800° C. for 4 hours in an atmosphere of 95% nitrogen and5% oxygen and then heat-treating the silicon wafer at a temperature of1000° C. for 16 hours in the same atmosphere, is equal to or less than10.

MCLT scanning of the wafer results in the distribution of the MCLTvalues, which are measured at all the in-plane positions of the wafer.The top 10% and the bottom 10% portions of the MCLT distribution arediscarded. In the remaining distribution, the highest MCLT value isdetermined as the maximum value, and the lowest MCLT value is determinedas the minimum value.

MCLT scanning is described in detail in Korean Patent Registration No.246816, a more detailed explanation of which is omitted herein.

Particularly, the difference between maximum and minimum values of thescale bar in the image obtained as a result of MCLT scanning can becontrolled to be equal to or less than 5, and more preferably, 3.

Here, a smaller difference between the maximum and minimum values of thescale bar in the image obtained as a result of MCLT scanning means moreuniform distribution of values of the MCLT within the silicon wafer. Adifference between maximum and minimum values of the scale bar of 0means that the in-plane MCLTs are the same, which is the most idealcase. Therefore, it is meaningless to define the lowest limit of thedifference between maximum and minimum values of the scale bar, and asmaller difference between maximum and minimum scale bars is desirable.

In this way, the control of the sizes of the maximal horizontaldirection width and the maximal vertical direction depth of the corecell in the silicon melt convection to provide a silicon wafer havinguniform in-plane quality can be achieved by adjusting an amount ofinflow of Ar gas flowing into the inside of the silicon single crystalingot growth apparatus, a rotation speed of the quartz crucible, or arotation speed of the silicon single crystal ingot.

At this time, optimal process variables for the growth of the siliconsingle crystal ingot having the uniform quality in the radial directionare not limited to only the amount of inflow of the Ar gas, the rotationspeed of the quartz crucible, or the rotation speed of the siliconsingle crystal ingot. Other appropriate process variables can beemployed depending on a diameter of a silicon single crystal ingot to begrown, a volume of a quartz crucible, a desired quality of a wafer, etc.

The following experimental examples show an effect of the amount ofinflow of the Ar gas, the rotation speed of the quartz crucible, and therotation speed of the silicon single crystal ingot on the quality in theradial direction of the silicon single crystal ingot.

EXPERIMENTAL EXAMPLE 1

First, in growing the silicon single crystal ingot based on theCzochralski method, the convection distribution of the silicon melt wasobserved for a case (Ar1) in which an amount of inflow of Ar gas was 50lpm (liter per min) and a case (Ar2) in which an amount of inflow of Argas was 100 lpm, under the conditions that the rotation speed of thequartz crucible was about 1.5 rpm (rotation per min) and the rotationspeed of the silicon single crystal ingot was 18 rpm.

FIG. 4 a is a schematic view showing the convection distribution of thesilicon melt in experimental example 1. As a result of experimentalexample 1, in the case (Ar1) that the amount of inflow of the Ar gas was50 lpm, maximal horizontal direction width W1max of core cell A1 was notover an edge portion of the solid-liquid interface at which the siliconsingle crystal was grown, and maximal vertical direction depth H1max ofcore cell A1 was less than 50% of the maximal depth of the silicon melt,as shown in the left side of a center axis of the silicon single crystalingot in FIG. 4 a.

On the other hand, in the case (Ar2) that the amount of inflow of the Argas was 100 lpm, maximal horizontal direction width W1′max of core cellA1′ was over an edge portion of the solid-liquid interface and occupiedabout 50% of the surface radius of the silicon melt, and maximalvertical direction depth H1′max of core cell A1′ occupied about 80% ofthe maximal depth of the silicon melt, as shown in the right side of acenter axis of the silicon single crystal ingot in FIG. 4 a.

Therefore, it can be seen that the size of outer cell B1′ in the rightside became smaller than that of outer cell B1 in the left side.

Through experimental example 1 as described above, it can be seen thatthe size of the core cell of the convection distribution of the siliconmelt can be enlarged by increasing the amount of inflow of the Ar gasflowing into the silicon single crystal ingot growth apparatus.

EXPERIMENTAL EXAMPLE 2

Next, the convection distribution of the silicon melt was observed for acase that the rotation speed of the quartz crucible was 4 rpm, and for acase that the rotation speed of the quartz crucible was 0.5 rpm, underthe conditions that the amount of inflow of the Ar gas was 70 lpm andthe rotation speed of the silicon single crystal ingot was 18 rpm. Aresult of the observation is shown in FIG. 4 b.

In the case that the rotation speed of the quartz crucible was 4 rpm,maximal horizontal direction width W2max of core cell A2 was not over anedge portion of the silicon single solid-liquid interface and maximalvertical direction depth H2 max of core cell A2 was less than 50% of themaximal depth of the silicon melt, as shown in the left side of FIG. 4b.

On the other hand, in the case that the rotation speed of the quartzcrucible was 0.5 rpm, maximal horizontal direction width W2′max of corecell A2′ occupied about 50% of the surface radius of the silicon melt,and maximal vertical direction depth H2′max of core cell A2′ occupiedabout 90% of the maximal depth of the silicon melt, as shown in theright side of FIG. 4 b.

Therefore, it can be seen that the size of outer cell B2′ in the rightside gets smaller than that of outer cell B2 in the left side.

Through experimental example 2 as described above, it can be seen thatthe size of the core cell of the convection distribution of the siliconmelt can be enlarged by decreasing the rotation speed of the quartzcrucible, which is a part of the silicon single crystal ingot growthapparatus.

EXPERIMENTAL EXAMPLE 3

Next, the convection distribution of the silicon melt was observed for acase in which the rotation speed of the silicon single crystal ingot was20 rpm, and for a case in which the rotation speed of the silicon singleingot was 12 rpm, under the conditions that the amount of inflow of theAr gas was 70 lpm and the rotation speed of the quartz crucible was 0.1rpm. A result of the observation is shown in FIG. 4 c.

In the case that the rotation speed of the silicon single crystal ingotwas 20 rpm, the silicon melt was circulated in contact with a part of acenter portion of the bottom of the quartz crucible in a state wheremaximal horizontal direction width W3max of core cell A3 was equal to ormore than about 50% of the surface radius of the silicon melt, andmaximal vertical direction depth H3max of core cell A3 was approximately100% of the maximal depth of the silicon melt, as shown in the left sideof FIG. 4 c.

On the other hand, in the case that the rotation speed of the siliconsingle crystal ingot was 12 rpm, maximal horizontal direction widthW3′max of core cell A3′ occupied about 50% of the surface radius of thesilicon melt, and maximal vertical direction depth H3′max of core cellA3′ occupied about 90% of the maximal depth of the silicon melt, asshown in the right side of FIG. 4 c.

Therefore, it can be seen that the size of outer cell B3′ in the rightside became larger than that of outer cell B3 in the left side.

Through experimental example 3 as described above, it can be seen thatthe size of the core cell of the convection distribution of the siliconmelt can be enlarged by increasing the rotation speed of the siliconsingle crystal ingot.

From the results of experimental examples as described above, it can beseen that the size of the core cell of the convection distribution ofthe silicon melt can be enlarged by increasing the amount of inflow ofthe Ar gas, decreasing the rotation speed of the quartz crucible, orincreasing the rotation speed of the silicon single crystal ingot.

On the contrary, the size of the core cell of the convectiondistribution of the silicon melt can be reduced by decreasing the amountof inflow of the Ar gas, increasing the rotation speed of the quartzcrucible, or decreasing the rotation speed of the silicon single crystalingot.

This means that the convection distribution of the silicon melt underthe growth of the silicon single crystal ingot, i.e., relative sizedistribution of the core cell and the outer cell, can be properlycontrolled by adjustment of process variables, particularly the amountof inflow of the Ar gas, the rotation speed of the quartz crucible, orthe rotation speed of the silicon single crystal ingot under growth.

However, the amount of inflow of the Ar gas, the rotation speed of thequartz crucible, or the rotation speed of the silicon single crystalingot, which are process variables for controlling the relative sizedistribution of the core cell and the outer cell in the convectiondistribution of the silicon melt, are only examples. These processvariables are not limitative, but other process variables can beadopted.

Now, the present invention will be described in more detail by way ofexemplary embodiments.

Embodiment 1

In embodiment 1 of the present invention, the silicon single crystalingot was grown under a state where the amount of inflow of the Ar gasflowing into the silicon single crystal ingot growth apparatus was 100lpm, the rotation speed of the silicon single crystal ingot under growthwas 18 rpm, and the rotation speed of the quartz crucible was 1.5 rpm.

According to embodiment 1, the maximal horizontal direction width Wmaxof core cell Ao was about 45% of the surface radius of the silicon melt,and the maximal vertical direction depth Hmax of core cell Ao was about80% of the maximal depth of the silicon melt.

Distribution of initial interstitial oxygen concentration [Oi] for adistance in a radial direction of a silicon wafer prepared by slicingand polishing the produced silicon single crystal ingot was measured. Aresult of the measurement is shown in FIG. 5 a.

In addition, comparative example 1 for producing the silicon singlecrystal ingot according to the conventional method, as shown in FIG. 2,was carried out. Distribution of initial interstitial oxygenconcentration [Oi] for a silicon wafer prepared from a silicon singlecrystal ingot produced in comparative example 1 was measured by the samemethod as in embodiment 1. A result of the measurement is shown in FIG.6 a.

As shown in FIG. 5 a, it can be confirmed that radial directiondistribution of the initial interstitial oxygen concentration in thesilicon wafer prepared according to an embodiment of the presentinvention exhibited a nearly uniform characteristic.

In contrast to this, as shown in FIG. 6 a, it can be confirmed that theinitial interstitial oxygen concentration in the radial direction in thesilicon wafer prepared according to comparative example 1 was reducedfrom a center to an edge of the silicon wafer.

Next, for 10 silicon wafers prepared according to embodiment 1 of thepresent invention, the initial interstitial oxygen concentration at 20points in each wafer was measured in order to obtain standarddeviations. The obtained standard deviations are listed in Table 1.

For 10 silicon wafers prepared according to comparative example 1, theinitial 10 interstitial oxygen concentration was measured in the sameway as in embodiment 1 in order to obtain standard deviations. Theobtained standard deviations are also listed in Table 1. TABLE 1 Wafer 12 3 4 5 6 7 8 9 10 Average Embodiment 1 0.033 0.031 0.027 0.041 0.0390.028 0.039 0.025 0.023 0.032 0.032 Wafer 1 2 3 4 5 6 7 8 9 10 AverageComparative 0.161 0.173 0.159 0.181 0.175 0.163 0.167 0.180 0.188 0.1760.172 example 1

As shown in Table 1, for embodiment 1 of the present invention, allstandard deviations of in-plane initial interstitial oxygenconcentration distribution of wafers are equal to or less than 0.041.

On the contrary, in comparative example 1, all standard deviations ofin-plane initial interstitial oxygen concentration distribution ofwafers exceed 0.1.6.

Next, after the wafers prepared according to embodiment 1 of the presentinvention were first heat-treated at a temperature of 800° C. for 4hours under an atmosphere of 95% nitrogen and 5% oxygen, and thenheat-treated at a temperature of 1000° C. for 16 hours in the sameatmosphere as the first heat-treatment, the interstitial oxygenconcentration was measured. The delta [Oi], which is a differencebetween the interstitial oxygen concentration before the heat-treatmentsand that after the heat-treatments, was measured for a distance in awafer radial direction. A result of the measurement is shown in FIG. 5b.

The same heat-treatment was performed for comparative example 1. Thedelta [Oi] was measured for a distance in a wafer radial direction, anda result of the measurement is shown in FIG. 6 b.

As shown in FIG. 5 b, in the wafers prepared according to embodiment 1of the present invention, it can be confirmed that the delta [Oi] wasvery uniform in a radial direction and a variation of the delta in theradial direction was equal to or less than 0.5 ppma.

On the contrary, as shown in FIG. 6 b, in comparative example 1, it canbe confirmed that the delta [Oi] was very nonuniform in the radialdirection. This is because a center portion, a peripheral portion, andan intermediate portion between the center and peripheral portion in aliquid at the vicinity of the solid-liquid interface have different heatdistributions during the crystal growth of the silicon single crystalingot in the conventional method described earlier. Therefore, thesilicon wafer obtained by processing the silicon single crystal ingot IGgrown from the liquid also has nonuniform quality.

On the other hand, after the silicon wafer prepared according toembodiment 1 of the present invention also heat-treated under theabove-mentioned conditions, MCLT scanning was performed. An imageobtained as a result of the MCLT scanning is shown in FIG. 5 c.

For comparative example 1, the MCLT scanning was performed in the sameway as in embodiment 1. An image obtained as a result of the MCLTscanning is shown in FIG. 6 c.

As shown in FIG. 5 c, the result of the MCLT scanning for the siliconwafer prepared according to embodiment 1 of the present invention showsa difference of 1.173 or so between the maximal and minimal scale bars.It can be seen from this result that the wafer quality is very uniform.

On the other hand, as shown in FIG. 6 c, the silicon Wafer preparedaccording to comparative example 1 shows a difference of about 18between the maximal and minimal scale bars. This value is very largecompared to embodiment 1 of the present invention. Accordingly, it canbe seen that the quality of the wafer according to comparative example 1was very nonuniform compared to embodiment 1 of the present invention.

Embodiment 2

A silicon single crystal ingot was grown under the conditions ofexperimental example 2 described earlier. Two conditions of experimentalexample 2 are defined as embodiment 2 and comparative example 2,respectively.

Namely, in embodiment 2, the silicon single crystal ingot was grownthrough the control of convection distribution of the silicon melt underthe conditions that the amount of inflow of the Ar gas flowing into thesilicon single crystal ingot growth apparatus was 70 lpm, the rotationspeed of the silicon single crystal ingot under growth was 18 rpm, andthe rotation speed of the quartz crucible was 0.5 rpm.

According to embodiment 2, the maximal horizontal direction width of thecore cell of the convection distribution of the silicon melt occupiedabout 50% of the surface radius of the silicon melt, and the maximalvertical direction depth of the core cell occupied about 90% of themaximal depth of the silicon melt.

In comparative example 2, the silicon single crystal ingot was grownunder the same conditions as in embodiment 2 for the amount of inflow ofthe Ar gas and the rotation speed of the silicon single crystal ingot,except that the rotation speed of the quartz crucible was 4 rpm.

According to comparative example 2, the maximal horizontal directionwidth of the core cell of the convection distribution of the siliconmelt was not over an edge portion of the silicon single solid-liquidinterface, and the maximal vertical direction depth of the core cell wasless than 50% of the maximal depth of the silicon melt.

In embodiment 2 and comparative example 2, a comparison between yield(%) of embodiment 2 and that of comparative example 2 is listed in thefollowing Table 2. Here, the yields are compared on the basis of asingle crystallization ratio, which is referred to as a ratio of asingle crystallized amount of silicon to an actual input amount ofpoly-crystalline silicon. In addition, an average yield comparison islisted in Table 2 after 10 of each silicon single crystal ingots weregrown and measured. TABLE 2 Rot number 1 2 3 4 5 6 7 8 9 10 AverageEmbodiment 2 80 80 62 80 80 80 80 80 80 80 78 Comparative 61 59 80 80 6460 80 55 53 80 67 example 2

As shown in Table 2, in embodiment 2 of the present invention, thesingle crystallization ratios of silicon single crystal ingots reached80% for the most part, and an average value reached about 78%. On theother hand, in comparative example 2, an average of the singlecrystallization ratios of silicon single crystal ingots reached 67%,which is relatively low.

Accordingly, it can be seen from Table 2 that embodiment 2 of thepresent invention achieves more single crystallization, i.e., a higheryield, by about 11% on average, compared to the conventional method.

As described above, the present invention provides a method forproducing a silicon single crystal ingot based on a Czochralski method,which is capable of providing a silicon single crystal ingot havinguniform quality in a radial direction and silicon wafers having uniformin-plane quality, by controlling convection distribution of a siliconmelt within a quartz crucible such that distribution of concentration ofoxygen flowing into the silicon single crystal ingot and distribution ofpoint defects become uniform.

In addition, the present invention discovered that the convectiondistribution of the silicon melt should be controlled in order to grow asilicon single crystal ingot having uniform quality in the radialdirection. Based on such a discovery, the present invention determinedcritical process variables for growing a silicon single crystal ingothaving uniform quality in the radial direction by controlling theconvection distribution through adjustment of an amount of inflow of anAr gas, a rotation speed of the quartz crucible, a rotation speed of thesilicon single crystal ingot, etc.

In addition, the present invention determined optimal process conditionsfor growing a silicon single crystal ingot having uniform quality in theradial direction.

Furthermore, the present invention increases semiconductor device yield,compared to conventional methods, which results in savings in productioncost of silicon wafers.

Although exemplary embodiments of the present invention have beendescribed in detail hereinabove, it should be clearly understood thatmany variations and/or modifications of the basic inventive conceptsherein taught which may appear to those skilled in the present art willstill fall within the spirit and scope of the present invention, asdefined in the appended claims.

1. A silicon wafer prepared from a silicon single crystal ingot grown bya Czochralski method, wherein a standard deviation of interstitialoxygen concentration distribution in a plane is equal to or less than0.1.
 2. The silicon wafer of claim 1, wherein a point defectconcentration contained in the silicon wafer is 10¹¹-10¹³/cm³.
 3. Thesilicon wafer of claim 1, wherein an in-plane variation of deltainterstitial oxygen concentration, which is a difference betweeninterstitial oxygen concentration after firstly heat-treating thesilicon wafer at a temperature of 800° C. for 4 hours in an atmosphereof 95% nitrogen and 5% oxygen and secondly heat-treating at atemperature of 1000° C. for 16 hours in an atmosphere of 95% nitrogenand 5% oxygen, and interstitial oxygen concentration before the firstheat-treatment, is equal to or less than 0.5 ppma.
 4. The silicon waferof claim 1, wherein a difference between maximum and minimum of a scalebar in an image obtained by MCLT (minority carrier life time) scanning,after firstly heat-treating the silicon wafer at a temperature of 800°C. for 4 hours in an atmosphere of 95% nitrogen and 5% oxygen andsecondly heat-treating the silicon wafer at a temperature of 1000° C.for 16 hours in an atmosphere of 95% nitrogen and 5% oxygen, is equal toor less than
 10. 5. The silicon wafer of claim 4, wherein the differencebetween maximum and minimum of a scale bar in an image obtained by MCLT(minority carrier life time) scanning, after firstly heat-treating thesilicon wafer at a temperature of 800° C. for 4 hours in an atmosphereof 95% nitrogen and 5% oxygen and secondly heat-treating the siliconwafer at a temperature of 1000° C. for 16 hours in an atmosphere of 95%nitrogen and 5% oxygen, is equal to or less than
 5. 6. The silicon waferof claim 5, wherein the difference between maximum and minimum of ascale bar in an image obtained by MCLT (minority carrier life time)scanning, after firstly heat-treating the silicon wafer at a temperatureof 800° C. for 4 hours in an atmosphere of 95% nitrogen and 5% oxygenand secondly heat-treating the silicon wafer at a temperature of 1000°C. for 16 hours in an atmosphere of 95% nitrogen and 5% oxygen, is equalto or less than
 3. 7. A silicon single crystal ingot wherein a standarddeviation of interstitial oxygen concentration distribution in a radialdirection of the silicon single crystal ingot is equal to or less than0.1.
 8. The silicon single crystal ingot of claim 7, wherein a pointdefect concentration contained in the silicon single crystal ingot is10¹¹-10¹³/cm³.